Square head and hex head bolts and screws, as one of the most widely used fasteners, typically adhere to the ASME B18.2.1 standard. This standard has become a guideline followed by engineers, procurement personnel, and manufacturers. This article will comprehensively interpret the product types and specifications included in the ASME B18.2.1 standard, assisting you in making informed choices to ensure project quality and compliance.
Fasteners are widely used in industries such as industrial manufacturing, heavy equipment, steel structure buildings, and infrastructure, and play a crucial role. The quality of fasteners directly determines the integrity and safety of the entire project.
Introduction to ASME B18.2.1 Standard
ASME B18.2.1：”Square and Hex Bolts and Screws (Inch Series)”, is a core standard issued by the American Society of Mechanical Engineers. It defines the dimensions, mechanical properties, materials, and testing requirements for square and hex head bolts and screws with nominal diameters ranging from 1/4 inch to 4 inches.
Standard Scope
Standardization: Unified product dimensions ensure interchangeability between bolts.
Safety: Strictly stipulate the mechanical properties, marking, and testing methods of hex bolts to ensure their load-bearing capacity and safety factor.
Authoritativeness: This standard is widely recognized and cited globally.
Specification Requirements
The standard specifies the dimensions, tolerance range, and thread requirements of the product in detail. It usually conforms to the ASME B1.1 unified standard threads and head markings.
It is used in conjunction with material standards such as ASTM A193, together forming a comprehensive specification covering everything from dimensions to performance.
Types and Dimensions of ASME B18.2.1 Standard
The products covered by the ASME B18.2.1 standard primarily fall into two categories: bolts and screws. The core distinction lies in the fact that bolts are typically used in conjunction with nuts, whereas screws are usually threaded into the internal threads of the connected components.
The dimensions of all products covered by this standard strictly adhere to the corresponding product dimension parameter table in the standard; key parameters include: nominal diameter, threads per inch, bolt/screw length, head width across flats, head thickness, thread length, etc. When selecting models, it is necessary to refer to the standard dimension table to ensure compatibility.
Types of ASME B18.2.1 Standard Bolt
Hex Bolt/Heavy Hex Bolt:
Hex bolt: The most common universal fastener, featuring a hex head that facilitates tightening from various angles using a wrench. With a complete range of sizes, it is the basic choice for steel structure connections and mechanical assembly.
Dimension of Hex Head Bolt
| Nominal Size or Basic Product Diameter | E | F | G | H | R | Lr | |||||||||
| Full-Size Body Diameter | Width Across Flats | Width Across Corners | Head Height | Radius of Fillet | Nominal Thread Length for Bolt Lengths | ||||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | Max | Min | ≤6 in | >6 in | ||
| 1/4 | 0.2500 | 0.260 | 0.237 | 7/16 | 0.438 | 0.425 | 0.505 | 0.484 | 1/16 | 0.188 | 0.150 | 0.030 | 0.010 | 0.750 | 1.000 |
| 5/16 | 0.3125 | 0.324 | 0.298 | 1/2 | 0.500 | 0.484 | 0.577 | 0.552 | 7/32 | 0.235 | 0.195 | 0.030 | 0.010 | 0.875 | 1.125 |
| 3/8 | 0.3750 | 0.388 | 0.360 | 9/16 | 0.562 | 0.544 | 0.650 | 0.620 | 1/4 | 0.268 | 0.226 | 0.030 | 0.010 | 1.000 | 1.250 |
| 7/16 | 0.4375 | 0.452 | 0.421 | 5/8 | 0.625 | 0.603 | 0.722 | 0.687 | 19/64 | 0.316 | 0.272 | 0.030 | 0.010 | 1.125 | 1.375 |
| 1/2 | 0.5000 | 0.515 | 0.482 | 3/4 | 0.750 | 0.725 | 0.866 | 0.826 | 11/32 | 0.364 | 0.302 | 0.030 | 0.010 | 1.250 | 1.500 |
| 5/8 | 0.6250 | 0.642 | 0.605 | 15/16 | 0.938 | 0.906 | 1.083 | 1.033 | 27/64 | 0.444 | 0.378 | 0.060 | 0.020 | 1.500 | 1.750 |
| 3/4 | 0.7500 | 0.768 | 0.729 | 1-1/8 | 1.125 | 1.088 | 1.299 | 1.240 | 1/2 | 0.524 | 0.455 | 0.060 | 0.020 | 1.750 | 2.000 |
| 7/8 | 0.8750 | 0.895 | 0.852 | 1-5/16 | 1.312 | 1.269 | 1.516 | 1.447 | 37/64 | 0.604 | 0.531 | 0.060 | 0.020 | 2.000 | 2.250 |
| 1 | 1.0000 | 1.022 | 0.976 | 1-1/2 | 1.500 | 1.450 | 1.732 | 1.653 | 43/64 | 0.700 | 0.591 | 0.090 | 0.030 | 2.250 | 2.500 |
| 1-1/18 | 1.1250 | 1.149 | 1.098 | 1-11/16 | 1.688 | 1.631 | 1.949 | 1.859 | 3/4 | 0.780 | 0.658 | 0.090 | 0.030 | 2.500 | 2.750 |
| 1-1/4 | 1.2500 | 1.277 | 1.223 | 1-7/8 | 1.875 | 1.812 | 2.165 | 2.066 | 27/32 | 0.876 | 0.749 | 0.090 | 0.030 | 2.750 | 3.000 |
| 1-3/8 | 1.3750 | 1.404 | 1.345 | 2-1/16 | 2.062 | 1.994 | 2.382 | 2.273 | 29/32 | 0.940 | 0.810 | 0.09 | 0.03 | 3.000 | 3.250 |
| 1-1/2 | 1.5000 | 1.531 | 1.470 | 2-1/4 | 2.250 | 2.175 | 2.598 | 2.480 | 1 | 1.036 | 0.902 | 0.090 | 0.030 | 3.250 | 3.500 |
| 1-3/4 | 1.7500 | 1.785 | 1.716 | 2-5/8 | 2.625 | 2.538 | 3.031 | 2.893 | 1-5/32 | 1.196 | 1.054 | 0.120 | 0.040 | 3.750 | 4.000 |
| 2 | 2.0000 | 2.039 | 1.964 | 3 | 3.000 | 2.900 | 3.464 | 3.306 | 1-11/32 | 1.388 | 1.175 | 0.120 | 0.040 | 4.250 | 4.500 |
| 2-1/4 | 2.2500 | 2.305 | 2.214 | 3-3/8 | 3.375 | 3.262 | 3.897 | 3.719 | 1-1/2 | 1.548 | 1.327 | 0.190 | 0.060 | 4.750 | 5.000 |
| 2-1/2 | 2.5000 | 2.559 | 2.461 | 3-3/4 | 3.750 | 3.625 | 4.330 | 4.133 | 1-21/32 | 1.708 | 1.479 | 0.190 | 0.060 | 5.250 | 5.500 |
| 2-3/4 | 2.7500 | 2.827 | 2.711 | 4-1/8 | 4.125 | 3.988 | 4.763 | 4.546 | 1-13/18 | 1.869 | 1.632 | 0.190 | 0.060 | 5.750 | 6.000 |
| 3 | 3.0000 | 3.081 | 2.961 | 4-1/2 | 4.500 | 4.350 | 5.196 | 4.959 | 2 | 2.060 | 1.815 | 0.190 | 0.060 | 6.250 | 6.500 |
| 3-1/4 | 3.2500 | 3.335 | 3.210 | 4-7/8 | 4.875 | 4.712 | 5.629 | 5.372 | 2-3/16 | 2.251 | 1.936 | 0.190 | 0.060 | 6.750 | 7.000 |
| 3-1/2 | 3.5000 | 3.589 | 3.461 | 5-1/4 | 5.250 | 5.075 | 6.062 | 5.786 | 2-5/16 | 2.380 | 2.057 | 0.190 | 0.060 | 7.250 | 7.500 |
| 3-3/4 | 3.7500 | 3.858 | 3.726 | 5-5/8 | 5.625 | 5.437 | 6.495 | 6.198 | 2-1/2 | 2.572 | 2.241 | 0.190 | 0.060 | 7.750 | 8.000 |
| 4 | 4.0000 | 4.111 | 3.975 | 6 | 6.000 | 5.800 | 6.928 | 6.612 | 2-11/16 | 2.764 | 2.424 | 0.190 | 0.060 | 8.250 | 8.500 |
Heavy Hex Bolt
The width and thickness of the head of the heavy hexagonal bolt are greater than those of the standard hex bolt. Provides more space for the support surface and wrench tightening.
Dimension of ASME B18.2.1 Standard Heavy Hex Bolt
| Nominal Size or Basic Product Diameter | E | F | G | H | R | Lr | |||||||||
| Full-Size Body Diameter | Width Across Flats | Width Across Corners | Head Height | Radius of Fillet | Nominal Thread Length for Bolt Lengths | ||||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | Max | Min | ≤6 in | >6 in | ||
| 1/2 | 0.5000 | 0.515 | 0.482 | 7/8 | 0.875 | 0.850 | 1.010 | 0.969 | 11/32 | 0.364 | 0.302 | 0.03 | 0.01 | 1.250 | 1.500 |
| 5/8 | 0.6250 | 0.642 | 0.605 | 1-1/16 | 1.062 | 1.031 | 1.227 | 1.175 | 27/64 | 0.444 | 0.378 | 0.06 | 0.02 | 1.500 | 1.750 |
| 3/4 | 0.7500 | 0.768 | 0.729 | 1-1/4 | 1.250 | 1.212 | 1.443 | 1.383 | 1/2 | 0.524 | 0.455 | 0.06 | 0.02 | 1.750 | 2.000 |
| 7/8 | 0.8750 | 0.895 | 0.852 | 1-7/16 | 1.438 | 1.394 | 1.660 | 1.589 | 37/64 | 0.604 | 0.531 | 0.06 | 0.02 | 2.000 | 2.250 |
| 1 | 1.0000 | 1.022 | 0.976 | 1-5/8 | 1.625 | 1.575 | 1.876 | 1.796 | 43/64 | 0.700 | 0.591 | 0.09 | 0.03 | 2.250 | 2.500 |
| 1-1/8 | 1.1250 | 1.149 | 1.098 | 1-13/16 | 1.812 | 1.756 | 2.093 | 2.002 | 3/4 | 0.780 | 0.658 | 0.09 | 0.03 | 2.500 | 2.750 |
| 1-1/4 | 1.2500 | 1.277 | 1.223 | 2 | 2.000 | 1.938 | 2.309 | 2,209 | 27/32 | 0.876 | 0.749 | 0.09 | 0.03 | 2.750 | 3.000 |
| 1-3/8 | 1.3750 | 1.404 | 1.345 | 2-3/16 | 2.188 | 2.119 | 2.526 | 2.416 | 29/32 | 0.940 | 0.810 | 0.09 | 0.03 | 3.000 | 3.250 |
| 1-1/2 | 1.5000 | 1.531 | 1.470 | 2-3/8 | 2.375 | 2.300 | 2.742 | 2.622 | 1 | 1.036 | 0.902 | 0.09 | 0.03 | 3.250 | 3.500 |
| 1-3/4 | 1.7500 | 1.785 | 1.716 | 2-3/4 | 2.750 | 2.662 | 3.175 | 3.035 | 1-5/32 | 1.196 | 1.054 | 0.12 | 0.04 | 3.750 | 4.000 |
| 2 | 2.0000 | 2.039 | 1.964 | 2-1/8 | 3.125 | 3.025 | 3.608 | 3.449 | 1-11/32 | 1.388 | 1,175 | 0.12 | 0.04 | 4.250 | 4.500 |
| 2-1/4 | 2.2500 | 2.305 | 2.214 | 3-1/2 | 3.500 | 3.388 | 4.041 | 3.862 | 1-1/2 | 1.548 | 1.327 | 0.19 | 0.06 | 4.750 | 5.000 |
| 2-1/2 | 2.5000 | 2.559 | 2.461 | 3-7/8 | 3.875 | 3.750 | 4.474 | 4.275 | 1-21/32 | 1.708 | 1.479 | 0.19 | 0.06 | 5.250 | 5.500 |
| 2-3/4 | 2.7500 | 2.827 | 2.711 | 4-1/4 | 4.250 | 4.112 | 4.907 | 4.688 | 1-13/14 | 1.869 | 1.632 | 0.19 | 0.06 | 5.750 | 6.000 |
| 3 | 3.0000 | 3.081 | 2.961 | 4-5/8 | 4.625 | 4.475 | 5.340 | 5.102 | 2 | 2.060 | 1.815 | 0.19 | 0.06 | 6.250 | 6.500 |
Square Head Bolt
The head is square in shape. Its design allows for fastening using an adjustable wrench or simpler tools in the square hole it is sunk into, and prevents rotation during tightening. It is commonly used when the bolt head needs to be embedded into a base or traditional cast iron components.
Dimension of Square Head Bolt
| Nominal Size or Basic Product Diameter | E | F | G | H | R | Lr | |||||||||
| Full-Size Body Diameter | Width Across Flats | Width Across Corners | Head Height | Radius of Fillet | Nominal Thread Length for Bolt Lengths | ||||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | Max | Min | ≤6 in | >6 in | ||
| 1/4 | 0.2500 | 0.260 | 0.237 | 3/8 | 0.375 | 0.362 | 0.530 | 0.498 | 11/64 | 0.188 | 0.156 | 0.030 | 0.010 | 0.750 | 1.000 |
| 5/16 | 0.3125 | 0.324 | 0.298 | 1/2 | 0.500 | 0.484 | 0.707 | 0.665 | 13/64 | 0.220 | 0.186 | 0.030 | 0.010 | 0.875 | 1.125 |
| 3/8 | 0.3750 | 0.388 | 0.360 | 9/16 | 0.562 | 0.544 | 0.795 | 0.747 | 1/4 | 0.268 | 0.232 | 0.030 | 0.010 | 1.000 | 1.250 |
| 7/16 | 0.4375 | 0.452 | 0.421 | 5/8 | 0.625 | 0.603 | 0.884 | 0.828 | 19/64 | 0.316 | 0.278 | 0.030 | 0.010 | 1.125 | 1.375 |
 1/2 | 0.5000 | 0.515 | 0.482 | 3/4 | 0.750 | 0.725 | 1.061 | 0.995 | 21/64 | 0.348 | 0.308 | 0.030 | 0.010 | 1.250 | 1.500 |
| 5/8 | 0.6250 | 0.642 | 0.605 | 15/16 | 0.938 | 0.906 | 1.326 | 1.244 | 27/64 | 0.444 | 0.400 | 0.060 | 0.020 | 1.500 | 1.750 |
| 3/4 | 0.7500 | 0.768 | 0.729 | 1-1/8 | 1.125 | 1.088 | 1.591 | 1.494 | 1/2 | 0.524 | 0.476 | 0.060 | 0.020 | 1.750 | 2.000 |
| 7/8 | 0.8750 | 0.895 | 0.852 | 1-5/16 | 1.312 | 1.269 | 1.856 | 1.742 | 19/32 | 0.620 | 0.568 | 0.060 | 0.020 | 2.000 | 2.250 |
| 1 | 1.0000 | 1.022 | 0.976 | 1-1/2 | 1.500 | 1.450 | 2.121 | 1.991 | 21/32 | 0.684 | 0.628 | 0.090 | 0.030 | 2.250 | 2.500 |
| 1-1/8 | 1.1250 | 1.149 | 1.098 | 1-11/16 | 1.688 | 1.631 | 2.386 | 2.239 | 3/4 | 0.780 | 0.720 | 0.090 | 0.030 | 2.500 | 2.750 |
| 1-1/4 | 1.2500 | 1.277 | 1.223 | 1-7/8 | 1.875 | 1.812 | 2.652 | 2.489 | 27/32 | 0.876 | 0.812 | 0.090 | 0.030 | 2.750 | 3.000 |
| 1-3/8 | 1.3750 | 1.404 | 1.345 | 2-1/16 | 2.062 | 1.994 | 2.917 | 2.738 | 29/32 | 0.940 | 0.872 | 0.090 | 0.030 | 3.000 | 3.250 |
| 1-1/2 | 1.5000 | 1.531 | 1.470 | 2-1/4 | 2.250 | 2.175 | 3.182 | 2.986 | 1 | 1.036 | 0.964 | 0.090 | 0.030 | 3.250 | 3.500 |
Askew Head Bolts
Also known as “carriage bolts”, they feature a smooth round head and a square shank beneath the head. When the bolt passes through a hole, the square shank engages with wood or metal, preventing the bolt from rotating when the nut is tightened. They are widely used in wood structures, fences, furniture, and agricultural equipment.
Dimension of Askew Head Bolt
| Nominal Size or Basic Product Diameter | E | F | G | H₁ | H | R | S | Lr | ||||||||
| Body Diameter | Width Across Flats | Width Across Corners | Head Height | Mid Height | Radius of Fillet | Maximum Unthreaded Length | Norminal Threaded Length for Bolt Lengths | |||||||||
| Max | Min | Basic | Max | Min | Max | Min | Max | Min | Ref. | Max | Min | Max | ≤6 in | >6 in | ||
| 3/8 | 0.375 | 0.388 | 0.360 | 9/16 | 0.562 | 0.544 | 0.795 | 0.747 | 0.317 | 0.277 | 0.250 | 0.030 | 0.010 | 0.250 | 1.000 | 1.250 |
| 1/2 | 0.500 | 0.515 | 0.482 | 3/4 | 0.750 | 0.725 | 1.061 | 0.995 | 0.411 | 0.371 | 0.328 | 0.030 | 0.010 | 0.312 | 1.250 | 1.500 |
| 5/8 | 0.625 | 0.642 | 0.605 | 15/16 | 0.938 | 0.906 | 1.326 | 1.244 | 0.520 | 0.480 | 0.422 | 0.060 | 0.020 | 0.344 | 1.500 | 1.750 |
| 3/4 | 0.750 | 0.768 | 0.729 | 1-1/8 | 1.125 | 1.088 | 1.591 | 1.494 | 0.614 | 0.574 | 0.500 | 0.060 | 0.020 | 0.406 | 1.750 | 2.000 |
| 7/8 | 0.875 | 0.895 | 0.852 | 1-5/16 | 1.312 | 1.269 | 1.856 | 1.742 | 0.723 | 0.683 | 0.594 | 0.060 | 0.020 | 0.438 | 2.000 | 2.250 |
| 1 | 1.000 | 1.022 | 0.976 | 1-1/2 | 1.500 | 1.450 | 2.121 | 1.991 | 0.801 | 0.761 | 0.656 | 0.090 | 0.030 | 0.500 | 2.250 | 2.500 |
Types of ASME B18.2.1 Standard Screw
Hex Screw/Heavy Hex Screw
Similar in appearance to hex head bolts, but with threads formed on the entire or part of the shank. It can be directly screwed into threaded holes of workpieces or used in conjunction with nuts.
Dimension of Hex Cap Screw
| Nominal Size or Basic Product Diameter | E | F | G | H | J | Lr | Y | Maximum Total Runout of Bearing Surface FIM | ||||||||
| Body Diameter | Width Across Flats | Width Across Corners | Head Height | Minimum Wrenching Height | Nominal Thread Length for Screw Lengths | Transition Thread Length | ||||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | ≤6 in | >6 in | Reference | Max | |||
| 1/4 | 0.2500 | 0.2500 | 0.2450 | 7/16 | 0.438 | 0.428 | 0.505 | 0.488 | 5/32 | 0.163 | 0.150 | 0.106 | 0.750 | 1.000 | 0.250 | 0.010 |
| 5/16 | 0.3125 | 0.3125 | 0.3065 | 1/2 | 0.500 | 0.489 | 0.577 | 0.557 | 13/64 | 0.211 | 0.195 | 0.140 | 0.875 | 1.125 | 0.278 | 0.011 |
| 3/8 | 0.3750 | 0.3750 | 0.3690 | 9/16 | 0.562 | 0.551 | 0.650 | 0.628 | 15/64 | 0.243 | 0.226 | 0.160 | 1.000 | 1.250 | 0.312 | 0.012 |
| 7/16 | 0.4375 | 0.4375 | 0.4305 | 5/8 | 0.625 | 0.612 | 0.722 | 0.698 | 9/32 | 0.291 | 0.272 | 0.195 | 1.125 | 1.375 | 0.357 | 0.013 |
| 1/2 | 0.5000 | 0.5000 | 0.4930 | 3/4 | 0.750 | 0.736 | 0.866 | 0.840 | 5/16 | 0.323 | 0.302 | 0.215 | 1.250 | 1.500 | 0.385 | 0.014 |
| 9/16 | 0.5625 | 0.5625 | 0.5545 | 13/16 | 0.812 | 0.798 | 0.938 | 0.910 | 23/64 | 0.871 | 0.348 | 0.250 | 1.375 | 1.625 | 0.417 | 0.015 |
| 5/8 | 0.6250 | 0.6250 | 0.6170 | 15/18 | 0.938 | 0.922 | 1.083 | 1.051 | 25/64 | 0.403 | 0.378 | 0.269 | 1.500 | 1.750 | 0.455 | 0.017 |
| 3/4 | 0.7500 | 0.7500 | 0.7410 | 1-1/8 | 1.125 | 1.100 | 1.299 | 1.254 | 15/32 | 0.483 | 0.455 | 0.324 | 1.750 | 2.000 | 0.500 | 0.020 |
| 7/8 | 0.8750 | 0.8750 | 0.8660 | 1-5/16 | 1.312 | 1.285 | 1.516 | 1.465 | 35/64 | 0.563 | 0.531 | 0.378 | 2.000 | 2.250 | 0.556 | 0.023 |
| 1 | 1.0000 | 1.0000 | 0.9900 | 1-1/2 | 1.500 | 1.469 | 1.732 | 1.675 | 39/64 | 0.627 | 0.591 | 0.416 | 2.250 | 2.500 | 0.625 | 0.026 |
| 1-1/8 | 1.1250 | 1.1250 | 1.1140 | 1-11/16 | 1.688 | 1.631 | 1.949 | 1.859 | 11/16 | 0.718 | 0.658 | 0.461 | 2.500 | 2.750 | 0.714 | 0.029 |
| 1-1/4 | 1.2500 | 1.2500 | 1.2390 | 1-7/8 | 1.875 | 1.812 | 2.165 | 2.066 | 25/32 | 0.813 | 0.749 | 0.530 | 2.750 | 3.000 | 0.714 | 0.033 |
| 1-3/8 | 1.3750 | 1.3750 | 1.3630 | 2-1/16 | 2.062 | 1.994 | 2.382 | 2.273 | 27/32 | 0.878 | 0.810 | 0.569 | 3.000 | 3.250 | 0.833 | 0.036 |
| 1-1/2 | 1.5000 | 1.5000 | 1.4880 | 2-1/4 | 2.250 | 2.175 | 2.598 | 2.480 | 1-5/16 | 0.974 | 0.902 | 0.640 | 3.250 | 3.500 | 0.833 | 0.039 |
| 1-3/4 | 1.7500 | 1.7500 | 1.7380 | 2-5/8 | 2.625 | 2.538 | 3.031 | 2.893 | 1-3/32 | 1.134 | 1.054 | 0.748 | 3.750 | 4.000 | 1.000 | 0.046 |
| 2 | 2.0000 | 2.0000 | 1.9880 | 3 | 3.000 | 2.900 | 3.464 | 3.306 | 1-7/32 | 1.263 | 1.175 | 0.825 | 4.250 | 4.500 | 1.111 | 0.052 |
| 2-1/4 | 2.2500 | 2.2500 | 2.2380 | 3-3/8 | 3.375 | 3.262 | 3.897 | 3.719 | 1-3/8 | 1.423 | 1.327 | 0.933 | 5.000 | 1.111 | 0.059 | |
| 2-1/2 | 2.5000 | 2.5000 | 2.4880 | 3-3/4 | 3.750 | 3.625 | 4.330 | 4.133 | 1-17/32 | 1.583 | 1.479 | 1.042 | 5.500 | 1.250 | 0.065 | |
| 2-3/4 | 2.7500 | 2.7500 | 2.7380 | 4-1/8 | 4.125 | 3.988 | 4.763 | 4.546 | 1-11/16 | 1.744 | 1.632 | 1.151 | 6.000 | 1.250 | 0.072 | |
| 3 | 3.0000 | 3.0000 | 2.9880 | 4-1/2 | 4.500 | 4.350 | 5.196 | 4.959 | 1-7/8 | 1.935 | 1.815 | 1.290 | 6.500 | 1.250 | 0.079 | |
Heavy hex screws also offer larger head sizes, suitable for applications requiring higher pre-tightening force or contact surface bearing strength.
Dimension of Heavy Hex Screw
| Nominal Size or Basic Product Diameter | E | F | G | H | J | Lt | Y | Maximum Total Runout of Bearing Surface FIM | ||||||||
| Body Diameter | Width Across Flats | Width Across Corners | Head Height | Minimum Wrenching Height | Nominal Thread Length for Screw Lengths度 | Transition Thread Length | ||||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | ≤6 in | >6in | Reference | Max | |||
| 1/2 | 0.5000 | 0.5000 | 0.482 | 7/8 | 0.875 | 0.850 | 1.010 | 0.969 | 5/16 | 0.323 | 0.302 | 0.215 | 1.250 | 1.500 | 0.385 | 0.016 |
| 5/8 | 0.6250 | 0.6250 | 0.605 | 1-1/16 | 1.062 | 1.031 | 1.227 | 1.175 | 25/64 | 0.403 | 0.378 | 0.269 | 1.500 | 1.750 | 0.455 | 0.019 |
| 3/4 | 0.7500 | 0.7500 | 0.729 | 1-1/4 | 1.250 | 1.212 | 1.443 | 1.383 | 15/32 | 0.483 | 0.455 | 0.324 | 1.750 | 2.000 | 0.500 | 0.022 |
| 7/8 | 0.8750 | 0.8750 | 0.852 | 1-7/16 | 1.438 | 1.394 | 1.660 | 1.589 | 65/64 | 0.563 | 0.531 | 0.378 | 2.000 | 2.250 | 0.556 | 0.025 |
| 1 | 1.0000 | 1.0000 | 0.976 | 1-5/8 | 1.625 | 1.575 | 1.876 | 1.796 | 39/64 | 0.627 | 0.591 | 0.416 | 2.250 | 2.500 | 0.625 | 0.028 |
| 1-1/8 | 1.1250 | 1.1250 | 1.098 | 1-13/16 | 1.812 | 1.756 | 2.093 | 2.002 | 11/16 | 0.718 | 0.658 | 0.461 | 2.500 | 2.750 | 0.714 | 0.032 |
| 1-1/4 | 1.2500 | 1.2500 | 1.223 | 2 | 2.000 | 1.938 | 2.309 | 2.209 | 25/32 | 0.813 | 0.749 | 0.530 | 2.750 | 3.000 | 0.714 | 0.035 |
| 1-3/8 | 1.3750 | 1.3750 | 1.345 | 2-3/16 | 2.188 | 2.119 | 2.526 | 2.416 | 27/32 | 0.878 | 0.810 | 0.569 | 3.000 | 3.250 | 0.833 | 0.038 |
| 1-1/2 | 1.5000 | 1.5000 | 1.470 | 2-3/8 | 2.375 | 2.300 | 2.742 | 2.622 | 15/16 | 0.974 | 0.902 | 0.640 | 3.250 | 3.500 | 0.833 | 0.041 |
| 1-3/4 | 1.7500 | 1.7500 | 1.716 | 2-3/4 | 2.750 | 2.662 | 3.175 | 3.035 | 1-3/32 | 1.134 | 1.054 | 0.748 | 3.750 | 4.000 | 1.000 | 0.048 |
| 2 | 2.0000 | 2.0000 | 1.964 | 3-1/8 | 3.125 | 3.025 | 3.608 | 3.449 | 1-7/32 | 1.263 | 1.175 | 0.825 | 4.250 | 4.500 | 1.111 | 0.055 |
| 2-1/4 | 2.2500 | 2.2500 | 2.214 | 3-1/2 | 3.500 | 3.388 | 4.041 | 3.862 | 1-3/8 | 1.423 | 1.327 | 0.933 | … | 5.000 | 1.111 | 0.061 |
| 2-1/2 | 2.5000 | 2.5000 | 2.461 | 3-7/8 | 3.875 | 3.750 | 4.474 | 4.275 | 1-17/32 | 1.583 | 1.479 | 1.042 | … | 5.500 | 1.250 | 0.068 |
| 2-3/4 | 2.7500 | 2.7500 | 2.711 | 4-1/4 | 4.250 | 4.112 | 4.907 | 4.688 | 1-11/16 | 1.744 | 1.632 | 1.151 | … | 6.000 | 1.250 | 0.074 |
| 3 | 3.0000 | 3.0000 | 2.961 | 4-5/8 | 4.625 | 4.475 | 5.340 | 5.102 | 1-7/8 | 1.935 | 1.815 | 1.290 | … | 6.500 | 1.250 | 0.081 |
Square Lag Screw
Similar to square head bolts, but with a threaded shank. Commonly used in equipment that requires high torque tightening and where the head can be countersunk. Such as old machine tools and woodworking machinery.
Dimension of Square Lag Screw
| Nominal Size or Basic Product Diameter | E | F | G | H | S | R | ||||||||
| Body or Shoulder Diamete | Width Across Flats | Width Across Corners | Head Height | Minimum Shoulder Length | Radius of Fillet | |||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | Min | Max | Min | ||
| No.10 | 0.1900 | 0.1990 | 0.1780 | 9/32 | 0.2810 | 0.2710 | 0.3980 | 0.3720 | 1/8 | 0.1400 | 0.1100 | 0.0940 | 0.0300 | 0.0100 |
| 1/4 | 0.2500 | 0.2600 | 0.2370 | 3/8 | 0.3750 | 0.3620 | 0.5300 | 0.4980 | 11/64 | 0.1880 | 0.1560 | 0.0940 | 0.0300 | 0.0100 |
| 5/16 | 0.3125 | 0.3240 | 0.2980 | 1/2 | 0.5000 | 0.4840 | 0.7070 | 0.6650 | 13/64 | 0.2200 | 0.1860 | 0.1250 | 0.0300 | 0.0100 |
| 3/8 | 0.3750 | 0.3880 | 0.3600 | 9/16 | 0.5620 | 0.5440 | 0.7950 | 0.7470 | 1/4 | 0.2680 | 0.2320 | 0.1250 | 0.0300 | 0.0100 |
| 7/16 | 0.4375 | 0.4520 | 0.4210 | 5/8 | 0.6250 | 0.6030 | 0.8840 | 0.8280 | 19/64 | 0.3160 | 0.2780 | 0.1560 | 0.0300 | 0.0100 |
| 1/2 | 0.5000 | 0.5150 | 0.4820 | 3/4 | 0.7500 | 0.7250 | 1.0610 | 0.9950 | 21/64 | 0.3480 | 0.3080 | 0.1560 | 0.0300 | 0.0100 |
| 5/8 | 0.6250 | 0.6420 | 0.6050 | 1-5/16 | 0.9380 | 0.9060 | 1.3260 | 1.2440 | 27/64 | 0.4440 | 0.4000 | 0.3120 | 0.0600 | 0.0200 |
| 3/4 | 0.7500 | 0.7680 | 0.7290 | 1-1/8 | 1.1250 | 1.0880 | 1.5910 | 1.4940 | 1/2 | 0.5240 | 0.4760 | 0.3750 | 0.0600 | 0.0200 |
| 7/8 | 0.8750 | 0.8950 | 0.8520 | 1-5/16 | 1.3120 | 1.2690 | 1.8560 | 1.7420 | 19/32 | 0.6200 | 0.5680 | 0.3750 | 0.0600 | 0.0200 |
| 1 | 1.0000 | 1.0220 | 0.9760 | 1-1/2 | 1.5000 | 1.4500 | 2.1210 | 1.9910 | 21/32 | 0.6840 | 0.6280 | 0.6250 | 0.0900 | 0.0300 |
| 1-1/8 | 1.1250 | 1.1490 | 1.0980 | 1-11/16 | 1.6880 | 1.6310 | 2.3860 | 2.2390 | 3/4 | 0.7800 | 0.7200 | 0.6250 | 0.0900 | 0.0300 |
| 1-1/4 | 1.2500 | 1.2770 | 1.2230 | 1-7/8 | 1.8750 | 1.8120 | 2.6520 | 2.4890 | 27/32 | 0.8760 | 0.8120 | 0.6250 | 0.0900 | 0.0300 |
Hex Lag Screw
The rod end is equipped with a guiding tip, facilitating quick alignment and initial engagement with threaded holes. It is particularly suitable for situations where rapid installation is required on the assembly line, or for blind hole assembly that requires self-positioning.
Dimension of Hex Lag Screw
| Nominal Size or Basic Product Diameter | E | F | G | H | S | R | ||||||||
| Body or Shoulder Diamete | Width Across Flats | Width Across Corners | Head Height | Minimum Shoulder Length | Radius of Fillet | |||||||||
| Max | Min | Basic | Max | Min | Max | Min | Basic | Max | Min | Min | Max | Min | ||
| No.10 | 0.1900 | 0.1990 | 0.1780 | 9/32 | 0.2810 | 0.2710 | 0.3230 | 0.3090 | 1/8 | 0.1400 | 0.1100 | 0.0940 | 0.0300 | 0.0100 |
| 1/4 | 0.2500 | 0.2600 | 0.2370 | 7/16 | 0.4380 | 0.4250 | 0.5050 | 0.4840 | 11/64 | 0.1880 | 0.1500 | 0.0940 | 0.0300 | 0.0100 |
| 5/16 | 0.3125 | 0.3240 | 0.2980 | 1/2 | 0.5000 | 0.4840 | 0.5770 | 0.5520 | 7/32 | 0.2350 | 0.1950 | 0.1250 | 0.0300 | 0.0100 |
| 3/8 | 0.3750 | 0.3880 | 0.3600 | 9/16 | 0.5620 | 0.5440 | 0.6500 | 0.6200 | 1/4 | 0.2680 | 0.2260 | 0.1250 | 0.0300 | 0.0100 |
| 7/16 | 0.4375 | 0.4520 | 0.4210 | 5/8 | 0.6250 | 0.6030 | 0.7220 | 0.6870 | 19/64 | 0.3160 | 0.2720 | 0.1560 | 0.0300 | 0.0100 |
| 1/2 | 0.5000 | 0.5150 | 0.4820 | 3/4 | 0.7500 | 0.7250 | 0.8660 | 0.8260 | 11/32 | 0.3640 | 0.3020 | 0.1560 | 0.0300 | 0.0100 |
| 5/8 | 0.6250 | 0.6420 | 0.6050 | 15/16 | 0.9380 | 0.9060 | 1.0830 | 1.0330 | 27/64 | 0.4440 | 0.3780 | 0.3120 | 0.0600 | 0.0200 |
| 3/4 | 0.7500 | 0.7680 | 0.7290 | 1-1/8 | 1.1250 | 1.0880 | 1.2990 | 1.2400 | 1/2 | 0.5240 | 0.4550 | 0.3750 | 0.0600 | 0.0200 |
| 7/8 | 0.8750 | 0.8950 | 0.8520 | 1-5/16 | 1.3120 | 1.2690 | 1.5160 | 1.4470 | 37/64 | 0.6040 | 0.5310 | 0.3750 | 0.0600 | 0.0200 |
| 1 | 1.0000 | 1.0220 | 0.9760 | 1-1/2 | 1.5000 | 1.4500 | 1.7320 | 1.6530 | 43/64 | 0.7000 | 0.5910 | 0.6250 | 0.0900 | 0.0300 |
| 1-1/8 | 1.1250 | 1.1490 | 1.0980 | 1-11/16 | 1.6880 | 1.6310 | 1.9490 | 1.8590 | 3/4 | 0.7800 | 0.6580 | 0.6250 | 0.0900 | 0.0300 |
| 1-1/4 | 1.2500 | 1.2770 | 1.2230 | 1-7/8 | 1.8750 | 1.8120 | 2.1650 | 2.0660 | 27/32 | 0.8760 | 0.7490 | 0.6250 | 0.0900 | 0.0300 |
Application scope
Fasteners under the ASME B18.2.1 standard are widely used in fields demanding high safety and durability due to their high strength and reliability:
Steel Structure Buildings: The main frame connections of factories, bridges, stadiums, and other structures often utilize heavy-duty hexagonal bolts.
Heavy Machinery and Equipment: flange connections for construction machinery, mining equipment, pressure vessels, and wind turbine towers.
Transportation: Fastening of railway vehicles, truck chassis, and ship deck equipment.
Energy and Power: critical connection points for power plant structures, transmission towers, and oil rigs.
Infrastructure: Installation of highway guardrails, noise barriers, and large-scale storage systems.
For customers requiring standard or customized solutions, we recommend collaborating with professional suppliers when purchasing ASME B18.2.1 bolts. It is essential to provide complete details such as standard number, product type, dimensions, and material grade requirements. Such as ASTM A193, A307, A320, A354, A449, etc. to ensure absolute accuracy.